Radiation-cure removal type pressure-sensitive adhesive sheet

ABSTRACT

A radiation-cure removable type pressure-sensitive adhesive sheet includes: a pressure-sensitive adhesive layer made from a polyester-based pressure-sensitive adhesive composition containing a polyester including at least a lactic acid unit, a dibasic acid unit, and a glycol unit, a radiation-cure resin, a radiation reaction initiator, and a crosslinking agent. The dibasic acid unit includes a dimer acid, the polyester has a glass transition temperature of −70 to −20° C., a weight average molecular weight of 20,000 to 200,000, and a hydroxyl value of 1 to 60 mgKOH/g, the composition contains 30 to 70 parts by weight of the radiation-cure resin based on 100 parts by weight of the polyester and contains 3 to 10% by weight of the radiation reaction initiator based on the amount of the radiation-cure resin.

TECHNICAL FIELD

The invention relates to a radiation-cure removable typepressure-sensitive adhesive sheet.

BACKGROUND ART

Removable pressure-sensitive adhesive sheets are not used in finalproducts and generally incinerated after they are used duringprocessing, transportation and so on. Therefore, since there has been aconcern about the depletion of fossil resources or the increase incarbon dioxide due to combustion of fossil resources, which is a causeof global warming, they are required to be produced using plant-derivedalternative materials, which are so-called carbon neutral, so thatmeasures can be taken against that.

Synthetic rubbers and acryl-based pressure-sensitive adhesives have beenused as adhesive materials for the removable pressure-sensitive adhesivesheets (Patent Documents 1 and 2), and unfortunately, at present, noavailable plant-derived acryl-based pressure-sensitive adhesive has beenfound.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No.    2000-223453-   Patent Document 2: JP-A No. 2008-63492

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Thus, an object of the invention is to provide a radiation-cureremovable type pressure-sensitive adhesive sheet that is produced usinga plant-derived raw material, is global environmentally-friendly, hasstable adhesive properties before irradiation, and has good peelabilityafter exposure to radiation.

Means for Solving the Problems

As a result of earnest studies to solve the problems, the inventors havefound the radiation-cure removable type pressure-sensitive adhesivesheet described below and completed the invention.

Specifically, the invention is directed to a radiation-cure removabletype pressure-sensitive adhesive sheet, including: a pressure-sensitiveadhesive layer made from a polyester-based pressure-sensitive adhesivecomposition containing a polyester including at least a lactic acidunit, a dibasic acid unit, and a glycol unit, a radiation-cure resin, aradiation reaction initiator, and a crosslinking agent, wherein thedibasic acid unit includes a dimer acid, the polyester has a weightaverage molecular weight of 20,000 to 200,000 and a glass transitiontemperature of −70 to −20° C. as measured using a differential scanningcalorimeter at a temperature rise rate of 20° C./minute, the polyesterhas a hydroxyl value of 1 to 60 mgKOH/g, the adhesive compositioncontains 30 to 70 parts by weight of the radiation-cure resin based on100 parts by weight of the polyester, the adhesive composition contains3 to 10% by weight of the radiation reaction initiator based on theamount of the radiation-cure resin, and the pressure-sensitive adhesivelayer has a gel fraction of 20 to 80% by weight before exposure toradiation.

In the radiation-cure removable type pressure-sensitive adhesive sheetof the invention, the polyester preferably contains 10 to 50% by mole ofthe lactic acid unit and 50 to 90% by mole of the other components thanthe lactic acid unit, and the molar ratio of the dibasic acid unit tothe glycol unit is preferably 1:0.8 to 1:1.2.

In the radiation-cure removable type pressure-sensitive adhesive sheetof the invention, the dibasic acid unit preferably further includes analiphatic dibasic acid other than the dimer acid.

In the radiation-cure removable type pressure-sensitive adhesive sheetof the invention, the polyester preferably includes a tri- orpolyfunctional carboxylic acid and/or polyol component as a componentother than the lactic acid unit, the dibasic acid unit, and the glycolunit, and the polyester preferably has a dispersity (Mw/Mn) of 2.5 to10.0.

In the radiation-cure removable type pressure-sensitive adhesive sheetof the invention, the polyester preferably has an acid value of 5mgKOH/g or less.

In the radiation-cure removable type pressure-sensitive adhesive sheetof the invention, the pressure-sensitive adhesive layer preferably has astorage modulus of 1×10⁴ to 1×10⁷ Pa as measured using a dynamicviscoelasticity meter under the conditions of 23° C. and a frequency of1 Hz.

In the radiation-cure removable type pressure-sensitive adhesive sheetof the invention, the radiation-cure resin preferably has a part with amolecular weight of 100 to 10,000 between functional groups.

In the radiation-cure removable type pressure-sensitive adhesive sheetof the invention, the crosslinking agent is preferably a tri- orpolyfunctional polyisocyanate.

The radiation-cure removable type pressure-sensitive adhesive sheet ofthe invention preferably has an adhesive strength of 1.4 N/20 mm or morebefore exposure to radiation, and preferably has an adhesive strength of0.9 N/20 mm or less after exposure to radiation.

Effects of the Invention

According to the invention, a polyester produced with plant-derived rawmaterials including lactic acid and a dibasic acid is used to form apressure-sensitive adhesive sheet for removable applications. Therefore,in contrast to pressure-sensitive adhesive sheets produced using fossilresource (petroleum)-derived raw materials, the pressure-sensitiveadhesive sheet according to the invention can suppress the depletion offossil resources (petroleum) and can achieve carbon neutral status evenwhen it is used and then removed and incinerated. According to theinvention, radiation-cure removable type pressure-sensitive adhesivesheets having stable adhesive properties before exposure to radiationand also having good peelability after exposure to radiation can beadvantageously obtained.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

The polyester for use in the radiation-cure removable typepressure-sensitive adhesive sheet of the invention (including apressure-sensitive adhesive tape, a pressure-sensitive adhesive film, aroll material, or the like) contains at least, a lactic acid unit, adibasic acid unit, and a glycol unit. The method for synthesizing thepolyester is not restricted, and it can be synthesized using a knownpolymerization method.

Examples of the lactic acid unit include, but are not limited to,L-lactide, D-lactide, DL-lactide, meso-lactide, L-lactic acid, D-lacticacid, and DL-lactic acid. Among them, DL-lactide is preferred in view ofpolymerization reaction efficiency and solubility in solvents. Thepolyester with the desired properties can be obtained bycopolymerization with any of these lactic acid units. One of theselactic acid units may be used, or two or more of these lactic acid unitsmay be used in combination.

The content of the lactic acid unit in the polyester components ispreferably from 10 to 50% by mole, more preferably from 15 to 45% bymole. If it is less than 10% by mole, the pressure-sensitive adhesivelayer produced using the polyester may have reduced elastic modulus, sothat the adhesive properties of the pressure-sensitive adhesive may varywith time. If it is more than 50% by mole, the polyester may have a highglass transition temperature (Tg), which is not preferred because it maycause degradation of adhesive properties.

On the other hand, the content of the components other than the lacticacid unit in the polyester components is preferably from 50 to 90% bymole, more preferably from 55 to 85% by mole. If it is less than 50% bymole, the pressure-sensitive adhesive produced using the polyester mayhave low adhesive properties, and if it is more than 90% by mole, thepressure-sensitive adhesive produced using the polyester may havereduced cohesive strength, which is not preferred because the adheringstrength (adhesive strength) to the adherend (such as a backing orsubstrate) may decrease.

The dibasic acid unit includes a dimer acid. A hydrogenated dimer acidmay also be used to form the dimer acid unit. The polyester with goodadhesive properties can be obtained by copolymerization with any ofthese dibasic acid units. One of these dibasic acid units may be used,or two or more of these dibasic acid units may be used in combination.

In the polyester, the dibasic acid unit preferably further includes analiphatic dibasic acid other than the dimer acid. When an aliphaticdibasic acid other than the dimer acid is subjected to thecopolymerization, it can increase the compatibility between the dimeracid and lactic acid, so that they are expected to have increasedsolubility in solvents.

The aliphatic dibasic acid is typically, but not limited to, apolycarboxylic acid, an alkyl ester thereof, or an acid anhydridethereof.

Examples of the polycarboxylic acid include aliphatic and alicyclicdicarboxylic acids such as adipic acid, azelaic acid, sebacic acid,1,4-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylicacid, dodecenyl succinic anhydride, fumaric acid, succinic acid,dodecanedicarboxylic acid, hexahydrophthalic anhydride,tetrahydrophthalic anhydride, maleic acid, maleic anhydride, itaconicacid, and citraconic acid. In particular, sebacic acid, which can beobtained from plants, is preferred. One of these acids may be used, ortwo or more these acids may be used in combination.

An aromatic dibasic acid may also be used to such an extent that it doesnot degrade the properties of the polyester for use in theradiation-cure removable type pressure-sensitive adhesive sheet of theinvention. Examples of the aromatic dibasic acid include, but are notlimited to, terephthalic acid, isophthalic acid, orthophthalic acid,1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid,4,4′-diphenyldicarboxylic acid, 2,2′-diphenyldicarboxylic acid, and4,4′-diphenyletherdicarboxylic acid. One of these acids may be used, ortwo or more of these acids may be used in combination.

For example, the glycol unit to be used may be, but not limited to, analiphatic glycol. The use of an aliphatic glycol makes it possible toincrease the molecular weight of the polyester and to improve theadhesive properties and durability of the pressure-sensitive adhesiveproduced with the polyester.

Examples of the aliphatic glycol include ethylene glycol, 1,2-propyleneglycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol,1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,3-methyl-1,5-pentanediol, neopentyl glycol, diethylene glycol,dipropylene glycol, 2,2,4-trimethyl-1,5-pentanediol,2-ethyl-2-butylpropanediol, 1,9-nonanediol, 2-methyloctanediol,1,10-decanediol, 1,4-cyclohexanedimethanol, and1,2-cyclohexanedimethanol. In particular, 1,3-propanediol, which can beobtained from plants, is preferred. One of these glycols may be used, ortwo or more of these glycols may be used in combination.

Any other glycol unit than the aliphatic glycol may be used incombination with the aliphatic glycol to such an extent that it does notdegrade the properties of the polyester for use in the radiation-cureremovable type pressure-sensitive adhesive sheet of the invention.Examples of such a glycol include an ethylene oxide adduct and apropylene oxide adduct of bisphenol A, an ethylene oxide adduct and apropylene oxide adduct of hydrogenated bisphenol A, polytetramethyleneglycol, polypropylene glycol, polyethylene glycol, and polycarbonateglycol. One of these glycols may be used, or two or more of theseglycols may be used in combination.

The molar ratio of the dibasic acid unit to the glycol unit ispreferably 1:0.8 to 1:1.2, more preferably 1:0.9 to 1:1.1. If the molarratio is less than 1:0.8 (the content of the glycol unit is lower), ahigher acid value or a lower molecular weight may be obtained, and if itis higher than 1:1.2 (the content of the glycol unit is higher), a lowermolecular weight may be obtained, or the adhesive properties may tend todecrease, which is not preferred.

The polyester preferably further contains a tri- or polyfunctionalcarboxylic acid and/or polyol component as a component other than thelactic acid unit, the dibasic acid unit, and the glycol unit, and thepolyester preferably has a dispersity (Mw/Mn) of 2.5 to 10.0, morepreferably 2.5 to 9.5. When the dispersity is in the above range, theadhesive strength can be effectively increased, and thepressure-sensitive adhesive can be effectively prevented from beingtransferred to the adherend. When the tri- or polyfunctional carboxylicacid and/or polyol is added, the molecular weight of the polyester foruse in the invention can be further increased, so that thepressure-sensitive adhesive produced using the polyester can have goodadhesive properties. In the description, Mw represents weight averagemolecular weight, and Mn number average molecular weight.

Examples of the tri- or polyfunctional carboxylic acid include, but arenot limited to, trimellitic acid, pyromellitic acid,benzophenonetetracarboxylic acid, biphenyltetracarboxylic acid, ethyleneglycol bis(anhydrotrimellitate), and glycerol tris(anhydrotrimellitate).

Examples of the tri- or polyfunctional polyol include glycerin,trimethylolpropane, pentaerythritol, and polyglycerin.

In view of reactivity, the content of the tri- or polyfunctionalcarboxylic acid and/or polyol in the components of the polyester ispreferably from 0.01 to 10% by mole, more preferably from 0.1 to 5% bymole.

As far as the properties of the polyester for use in the radiation-cureremovable type pressure-sensitive adhesive sheet of the invention arenot degraded, glycolic acid or a lactone may also be copolymerized(used), or glycolic acid or a lactone may be added and polymerized afterthe polymerization of other components to modify the end of themolecule. An acid anhydride may also be added and polymerized after thepolymerization of other components to convert the end of the molecule toa carboxyl group. One of these may be used, or two or more of these maybe used in combination.

The polyester has a glass transition temperature (Tg) of −70 to −20° C.,preferably −60 to −40° C. as measured using a differential scanningcalorimeter at a temperature rise rate of 20° C./minute. If the Tg islower than −70° C., the holding power may decrease, and if the Tg ishigher than −20° C., the pressure-sensitive adhesive produced using thepolyester may have degraded adhesive properties at room temperature,which is not preferred.

The polyester has a weight average molecular weight of 20,000 to200,000, preferably 50,000 to 150,000. A weight average molecular weightof less than 20,000 may cause a reduction in the adhesive strength ofthe pressure-sensitive adhesive produced using the polyester. A weightaverage molecular weight of more than 200,000 is also not preferred,because it may cause a reduction in cohesive strength or in holdingpower.

The polyester has a hydroxyl value of 1 to 60 mgKOH/g, preferably 2 to40 mgKOH/g, in particular, preferably 3 to 20 mgKOH/g. If the hydroxylvalue is less than 1 mgKOH/g, the polyester will have low reactivitywith a crosslinking agent, which will be a cause of a reduction in thecohesive strength of the pressure-sensitive adhesive produced using thepolyester. A hydroxyl value of more than 60 mgKOH/g may cause areduction in water resistance and therefore is not preferred.

The polyester preferably has an acid value of 5 mgKOH/g or less, morepreferably 0.1 to 3 mgKOH/g. An acid value of more than 5 mgKOH/g maycause acceleration of hydrolysis and a reduction in durability, andtherefore is not preferred.

The polyester-based pressure-sensitive adhesive composition used for theradiation-cure removable type pressure-sensitive adhesive sheet of theinvention is preferably a polyester composition containing 50 to 100parts by weight of the polyester (polyester (i)) and 0 to 50 parts byweight of a branched polyester oligomer (ii) with a hydroxyl value of100 to 1,000 mgKOH/g, more preferably a polyester composition containing90 to 99 parts by weight of the polyester (i) and 1 to 10 parts byweight of a branched polyester oligomer (ii) with a hydroxyl value of100 to 800 mgKOH/g. The addition of the branched polyester oligomer (ii)is effective in accelerating curing (crosslinking) and in reducingstaining of the adherend after the removal, when the composition is usedto form the pressure-sensitive adhesive (layer). If the hydroxyl valueis less than 100 mgKOH/g, the curing-accelerating effect may beinsufficient, and a hydroxyl value of more than 1,000 mgKOH/g may causea reduction in solubility in general-purpose organic solvents, andtherefore is not preferred. The addition of the branched polyesteroligomer (ii) in an amount of more than 50 parts by weight may causedegradation of the adhesive properties, and therefore is not preferred.As used herein, the term “polyester composition” is intended to includea polyester alone (the case where only a polyester is used with nobranched polyester oligomer) or a mixture of a polyester and a branchedpolyester oligomer, and the term “polyester-based pressure-sensitiveadhesive composition” is intended to include a mixture containing thepolyester composition and an additive such as a crosslinking agent.

The branched polyester oligomer (ii) has a branched structure and goodsolubility in organic solvents, and is relatively cheap from an economicpoint of view.

The branched polyester oligomer (ii) preferably has a number averagemolecular weight of 1,000 to 8,000, more preferably 1,000 to 6,000. Anumber average molecular weight of less than 1,000 may be a cause ofstaining of the adherend, and a number average molecular weight of morethan 8,000 may cause a reduction in reactivity with a crosslinkingagent, and therefore is not preferred.

For example, the structure of the branched polyester oligomer (ii) ispreferably, but not limited to, a structure having a main skeletonobtained by polycondensation or polyaddition reaction of ABx compound.As used herein, the term “ABx compound” means a compound havingdifferent functional groups A and B (organic groups). The ABx compoundis also a compound having a functional group that does not causeintramolecular condensation or intramolecular addition reaction but cancause intermolecular condensation or intermolecular addition reaction.In particular, the main skeleton preferably has an ester bond. In thedifferent functional groups, for example, the functional group A is acarboxyl group or a derivative thereof, and the functional group B is ahydroxyl group or a derivative thereof, and the ABx compound is acompound having these groups.

Examples of the ABx compound include 2,2-dimethylolpropionic acid,2,2-dimethylolbutanoic acid, 5-(2-hydroxyethoxy)isophthalic acid,5-acetoxyisophthalic acid, 3,5-bis(2-hydroxyethoxy)benzoic acid,3,5-bis(2-hydroxyethoxy)benzoic acid methyl ester,4,4-(4′-hydroxyphenyl)pentanoic acid,5-hydroxycyclohexane-1,3-dicarboxylic acid,1,3-dihydroxy-5-carboxycyclohexane,5-(2-hydroxyethoxy)cyclohexane-1,3-dicarboxylic acid, and1,3-(2-hydroxyethoxy)-5-carboxycyclohexane. In particular,2,2-dimethylolpropionic acid or 2,2-dimethylolbutanoic acid is preferredin view of versatility of raw material compounds and ease ofpolymerization reaction process.

The branched polyester oligomer (ii) is also effective, because it hasan ester bond and therefore has good compatibility with the polyester(i) so that the product (crosslinked product) of the reaction betweenthem tends to have higher transparency. In particular, a branchedpolyester oligomer (ii) of an aliphatic monomer tends to have highercompatibility, and therefore is preferred.

The branched polyester oligomer (ii) can be produced by a methodincluding allowing the ABx compound alone to react in the presence of acondensation reaction catalyst to synthesize the oligomer. In addition,a polyol group-containing compound, a polycarboxylic acid, or a compoundhaving both a hydroxyl group and a carboxyl group may be used to formthe branched point of the branched polyester oligomer (ii).

Examples of the polyol group-containing compound include variousgeneral-purpose glycol compounds and tri- or polyfunctional hydroxylgroup-containing compounds such as trimethylolpropane, pentaerythritol,and dipentaerythritol.

Examples of the polycarboxylic acid include various general-purposedibasic acids and tri- or polyfunctional carboxylic acid compounds suchas trimellitic acid, pyromellitic acid, and benzophenonetetracarboxylicacid.

In addition, examples of the compound having both a hydroxyl group and acarboxyl group include glycolic acid, hydroxypivalic acid,3-hydroxy-2-methylpropionic acid, lactic acid, glyceric acid, malicacid, and citric acid.

Besides the polyol group-containing compound, the polycarboxylic acid,or the compound having both a hydroxyl group and a carboxyl group, astraight-chain (linear) polyester oligomer obtained by condensationreaction of a dibasic acid with a glycol compound, or a specificfunctional group-containing branched polyester oligomer (iii) obtainedby copolymerization of a dibasic acid, a glycol compound, and a tri- orpolyfunctional polyol group-containing compound or a polycarboxylic acidmay also be used to form the branched point of the branched polyesteroligomer (ii).

Any of various general-purpose dibasic acids, a glycol compound, a tri-or polyfunctional polycarboxylic acid, and a polyhydric alcohol compoundmay be used as a raw material for the straight-chain (linear) polyesteroligomer or the specific functional group-containing branched polyesteroligomer (iii) capable of forming the branched point.

Examples of the dibasic acid include aliphatic dibasic acids such assuccinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanoicacid; aromatic dibasic acids such as terephthalic acid, isophthalicacid, orthophthalic acid, 1,2-naphthalenedicarboxylic acid, and1,6-naphthalenedicarboxylic acid; and alicyclic dibasic acids such as1,2-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and4-methyl-1,2-cyclohexanedicarboxylic acid. Among them, particularly inview of heat resistance, terephthalic acid, isophthalic acid,orthophthalic acid, 1,2-naphthalenedicarboxylic acid, and1,6-naphthalenedicarboxylic acid are preferred, and terephthalic acid,1,2-naphthalenedicarboxylic acid, and 1,6-naphthalenedicarboxylic acidare particularly preferred.

Examples of the glycol compound include aliphatic diols such as ethyleneglycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol,1,3-butylene glycol, 2,3-butylene glycol, 1,4-butylene glycol,2-methyl-1,3-propylene glycol, neopentyl glycol, 3-methyl-1,5-pentadiol,2,2,4-trimethyl-1,3-pentanediol, 2,4-diethyl-1,5-pentanediol,2-ethyl-1,3-hexanediol,2,2-dimethyl-3-hydroxypropyl-2′,2′-dimethyl-3-hydroxypropanate,2-n-butyl-2-ethyl-1,3-propanediol, 3-ethyl-1,5-pentanediol,3-propyl-1,5-pentanediol, 2,2-diethyl-1,3-propanediol, and3-octyl-1,5-pentanediol; alicyclic glycols such as1,3-bis(hydroxymethyl)cyclohexane, 1,4-bis(hydroxymethyl)cyclohexane,1,4-bis(hydroxyethyl)cyclohexane, 1,4-bis(hydroxypropyl)cyclohexane,1,4-bis(hydroxymethoxy)cyclohexane, 1,4-bis(hydroxyethoxy)cyclohexane,2,2-bis(4-hydroxymethoxycyclohexyl)propane,2,2-bis(4-hydroxyethoxycyclohexyl)propane,bis(4-hydroxycyclohexyl)methane, 2,2-bis(4-hydroxycyclohexyl)propane,and 3(4),8(9)-tricyclo[5.2.1.O^(2,6)]decanedimethanol; and aromaticglycols such as ethylene oxide or propylene oxide adducts of bisphenol Aor the like.

In addition, examples of the tri- or polyfunctional polycarboxylic acidand the polyol group-containing compound include trimellitic acid,pyromellitic acid, benzophenonetetracarboxylic acid, glycerin,trimethylolpropane, and pentaerythritol.

Examples of the method for removing water produced by the polymerization(condensation) reaction include a method of removing water by azeotropewith toluene or xylene, a method including blowing inert gas into thereaction system so that the produced water and monoalcohol can bedischarged together with the inert gas to the outside of the reactionsystem, and a method of distillation under reduced pressure.

The polymerization catalyst used in the polymerization (condensation)reaction may be one commonly used in the production of polyesters, andexamples of such a catalyst include, but are not limited to, variousmetal compounds such as titanium-based, tin-based, antimony-based,zinc-based, and germanium-based compounds; and strong acid compoundssuch as p-toluenesulfonic acid and sulfuric acid.

In order to increase the compatibility with the polyester, it is morepreferred to introduce a long-chain hydrocarbon group of 6 or morecarbon atoms into the end group of the branched polyester oligomer. Forexample, a hydrocarbon group of 6 or more carbon atoms may be introducedby a method of performing addition reaction or condensation reaction ofa compound having a hydrocarbon group of 6 or more carbon atoms with theterminal carboxyl or hydroxyl group of the branched polyester oligomersynthesized previously. Examples of such a compound include amonoalcohol having a long-chain alkyl group, such as hexanol, octanol,decyl alcohol, undecyl alcohol, or dodecyl alcohol; and a monocarboxylicacid having a long-chain alkyl or alkenyl group, such as octanoic acid,decanoic acid, dodecanoic acid, myristic acid, palmitic acid, stearicacid, or oleic acid having an unsaturated group, or a methyl esterderivative thereof.

There are also a method of performing ring-opening addition of acarboxylic anhydride compound having a hydrocarbon group of 6 or morecarbon atoms to the terminal hydroxyl group in the presence of a basiccatalyst; and a method of performing addition reaction of a compoundhaving a glycidyl group and a hydrocarbon group of 6 or more carbonatoms with the terminal carboxyl group in the presence of an appropriatecatalyst such as triphenylphosphine. The compound having a hydrocarbongroup may be an acid anhydride compound, examples of which includedodecenylsuccinic anhydride and octadecylsuccinic anhydride. Examples ofthe compound having a glycidyl group include various aryl glycidylethers such as phenyl glycidyl ether; polyethylene glycol monoglycidylether, polypropylene glycol monoglycidyl ether, and polytetramethyleneglycol monoglycidyl ether; and monoglycidyl ethers such as alkyl,alkenyl, and alkynyl glycidyl ethers.

The polyester pressure-sensitive adhesive composition for use in theinvention contains at least the polyester or the polyester composition,a radiation-cure resin, a crosslinking agent, and a radiation reactioninitiator.

The radiation-cure resin may be an oligomer component capable of beingradically or cationically polymerized by radiation.

The part of the radiation-cure resin between the functional groupspreferably has a weight average molecular weight in the range of about100 to about 10,000, more preferably 1,000 to 5,000. The averagemolecular weight of the part between the functional groups can becalculated from the formula: (the weight average molecular weight of theradiation-cure resin)/{(the number of the functional groups in theradiation-cure resin)−1}, wherein the functional groups are intended toinclude double bond-containing functional groups reactive to radiation,such as vinyl groups capable of reacting upon exposure to radiation. Ifthe molecular weight of the part between the functional groups is morethan 10,000, there may be a long distance between the crosslinked pointsafter the reaction by exposure to radiation, and the degree ofcrosslinkage may be low, so that the adhesive strength may fail to bereduced to the desired level. If it is less than 100, crosslinkage mayfail to be formed, so that the adhesive strength may fail to be reduced,which is not preferred.

The oligomer component capable of being radically polymerized byradiation may be one obtained by adding two or more unsaturated doublebonds of (meth)acryloyl groups, vinyl groups, or the like to apolyethylene, polyester, epoxy, or urethane skeleton, such as polyester(meth)acrylate, epoxy (meth)acrylate, or urethane (meth)acrylate.

The polyester (meth)acrylate may be one obtained by allowing ahydroxyl-terminated polyester, which is obtained from a polyhydricalcohol and a polycarboxylic acid, to react with (meth)acrylic acid,(meth)acrylic acid chloride, glycidyl (meth)acrylate,2-methacryloyloxyethyl isocyanate, or the like, and examples of thepolyester (meth)acrylate include ARONIX M-6000, M-7000, M-8000, andM-9000 series manufactured by TOAGOGEI CO., LTD.

The epoxy (meth)acrylate may be one obtained by allowing epoxy resin toreact with hydroxyalkyl (meth)acrylate such as 2-hydroxyethyl acrylateor 4-hydroxybutyl acrylate, or (meth) acrylic acid, and examples of theepoxy (meth)acrylate include RIPOXY SP and VR series manufactured bySHOW A HIGHPOLYMER CO., LTD. and EPOXY ESTER series manufactured byKYOEISHA CHEMICAL Co., LTD.

The urethane (meth)acrylate may be one obtained by reaction of a polyol,an isocyanate, and hydroxyalkyl (meth)acrylate such as 2-hydroxyethylacrylate or 4-hydroxybutyl acrylate, and examples of the urethane(meth)acrylate include ART RESIN UN series manufactured by NegamiChemical Industrial Co., Ltd., NK OLIGO U series manufactured byShin-Nakamura Chemical Co., Ltd., and SHIKOH UV series manufactured byThe Nippon Synthetic Chemical Industry Co., Ltd.

The oligomer component capable of being cationically polymerized byradiation may be a compound having a cationically polymerizablefunctional group such as an epoxy group, a hydroxyl group, a vinyl ethergroup, an episulfide group, or an ethyleneimine group. Among them, anepoxy group-containing compound is preferably used because it has theadvantage of being highly reactive.

For example, the epoxy group-containing compound may be a glycidyl etherepoxy resin produced by reaction of a polyhydric phenol compound or apolyhydric alcohol with epichlorohydrin. Specific examples include adiglycidyl ether of bisphenol A or an alkylene oxide adduct thereof, adiglycidyl ether of bisphenol F or an alkylene oxide adduct thereof, adiglycidyl ether of hydrogenated bisphenol A or an alkylene oxide adductthereof, ethylene glycol diglycidyl ether, propylene glycol diglycidylether, neopentyl glycol diglycidyl ether, butanediol diglycidyl ether,hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether,polypropylene glycol diglycidyl ether, trimethylolpropane polyglycidylether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether,and resorcin diglycidyl ether.

The radiation-cure resin is contained in an amount of 30 to 70 parts byweight, preferably 40 to 60 parts by weight, based on 100 parts byweight of the polyester or the polyester composition (polyester-basedpolymer). If the amount of the radiation-cure resin is more than 70parts by weight, it will be not easy to mix the resin with the polyesterand so on, so that it will be difficult to obtain a pressure-sensitiveadhesive sheet (pressure-sensitive adhesive layer) with a goodappearance. An amount of less than 30 parts by weight is not preferred,because with such an amount, a sufficient reduction in adhesive strengthcannot be obtained after exposure to radiation.

A commercially-available, ultraviolet-cure resin material may also beused as the radiation-cure resin. In order to increase the biomassdegree, a biomass material may also be used to produce theradiation-cure resin.

A radiation reaction initiator is used when the polyester-basedpressure-sensitive adhesive composition containing the radiation-cureresin and so on is crosslinked (cured) by radiation such as ultravioletlight. Such a radiation reaction initiator may be a photo-radicalpolymerization initiator or a photo-cationic polymerization initiator.

Examples of the photo-radical polymerization initiator include α-ketolcompounds such as 4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-propyl)ketone,α-hydroxy-α,α′-dimethyl acetophenone, 2-methyl-2-hydroxypropiophenone,and 1-hydroxycyclohexyl phenyl ketone; acetophenone compounds such asmethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone,2,2-diethoxyacetophenone, and2-methyl-1-[4-(methylthio)-phenyl]-2-morpholinopropane-1; benzoin ethercompounds such as benzoin ethyl ether, benzoin isopropyl ether, andanisoin methyl ether; ketal compounds such as benzyl dimethyl ketal;aromatic sulfonyl chloride compounds such as 2-naphthalene sulfonylchloride; optically active oxime compounds such as1-(phenone-1,1-propanedione-2-(o-ethoxycarbonyl)oxime; benzophenonecompounds such as benzophenone, benzoylbenzoic acid, and3,3′-dimethyl-4-methoxybenzophenone; thioxanthone compounds such asthioxanthone, 2-chlorothioxanthone, 2-methyl thioxanthone, 2,4-dimethylthioxanthone, isopropyl thioxanthone, 2,4-dichlorothioxanthone,2,4-diethyl thioxanthone, and 2,4-diisopropyl thioxanthone; camphorquinone; halogenated ketone; acyl phosphinoxide; and acyl phosphonate.

Examples of the photo-cationic polymerization initiator includethioxanthones such as thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethyl thioxanthone, 2-ethyl thioxanthone,2,4-diethyl thioxanthone, and 2-isopropyl thioxanthone, benzil,dibenzosuberone, α-acyloxime ester, camphorquinone, sulfonyl ketone,titanocene, onium salts such as aromatic diazonium salts, aromaticiodonium salts, and aromatic sulfonium salts, organometallic complexessuch as iron-arene complexes, titanocene complexes, and arylsilanol-aluminum complexes, nitrobenzyl esters, sulfonic acidderivatives, phosphate esters, sulfonic acid derivatives, phosphateesters, phenolsulfonate esters, diazonaphthoquinone, andN-hydroxyimidosulfonate.

The radiation reaction initiator is mixed in an amount of 3 to 10% byweight, preferably 5 to 8% by weight, based on the amount of theradiation-cure resin. If the amount of the reaction initiator is lessthan 3% by weight, crosslinking (curing) will be insufficiently achievedby exposure to radiation, so that a reduction in adhesive strengthcannot be obtained. If the amount of the reaction initiator is more than10% by weight, the appearance of the pressure-sensitive adhesive sheet(pressure-sensitive adhesive layer) obtained in the process of applyingthe polyester-based pressure-sensitive adhesive composition will tend tobe degraded, which is not preferred.

The polyester-based pressure-sensitive adhesive composition used for theradiation-cure removable type pressure-sensitive adhesive sheet of theinvention contains a crosslinking agent. A pressure-sensitive adhesivelayer can be formed by subjecting the crosslinking agent-containingpressure-sensitive adhesive composition to a crosslinking reaction. Thecrosslinking agent to be used is not restricted and may be anyconventionally known one such as a polyvalent isocyanurate, apolyfunctional isocyanate, a polyfunctional melamine compound, apolyfunctional epoxy compound, a polyfunctional oxazoline compound, apolyfunctional aziridine compound, or a metal chelate compound. In apreferred mode, a polyvalent isocyanurate or a polyfunctional isocyanatecompound is used, particularly in view of the transparency of theresulting pressure-sensitive adhesive layer or the achievement of highgel fraction.

For example, the polyvalent isocyanurate may be a polyisocyanurate ofhexamethylene diisocyanate. The use of such a compound makes it possibleto achieve the object of obtaining a pressure-sensitive adhesive layerwith transparency and high gel fraction, and therefore is advantageous.Commercially available products of the polyvalent isocyanurate may alsobe used, examples of which include DURANATE TPA-100 (trade name,manufactured by Asahi Kasei Chemicals Corporation) and CORONATE HK,CORONATE HX, and CORONATE 2096 (trade names, manufactured by NipponPolyurethane Industry Co., Ltd.). One of these may be used, or two ormore of these may be used in combination.

The polyfunctional isocyanate compound is preferably, but not limitedto, a compound having at least two isocyanate groups, more preferablythree or more isocyanate groups in the molecule (when the compositioncontains the branched polyester oligomer (ii), it may have two or moreisocyanate groups), examples of which include aliphatic polyisocyanates,alicyclic polyisocyanates, and aromatic polyisocyanates. One of thesemay be used, or two or more of these may be used in combination.

Examples of the aliphatic polyisocyanates include 1,2-ethylenediisocyanate, tetramethylene diisocyanates such as 1,2-tetramethylenediisocyanate, 1,3-tetramethylene diisocyanate, and 1,4-tetramethylenediisocyanate; hexamethylene diisocyanates such as 1,2-hexamethylenediisocyanate, 1,3-hexamethylene diisocyanate, 1,4-hexamethylenediisocyanate, 1,5-hexamethylene diisocyanate, 1,6-hexamethylenediisocyanate, and 2,5-hexamethylene diisocyanate; and2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate,and lysine diisocyanate.

Examples of the alicyclic polyisocyanates include isophoronediisocyanate; cyclohexyl diisocyanates such as 1,2-cyclohexyldiisocyanate, 1,3-cyclohexyl diisocyanate, and 1,4-cyclohexyldiisocyanate; cyclopentyl diisocyanates such as 1,2-cyclopentyldiisocyanate and 1,3-cyclopentyl diisocyanate; hydrogenated xylylenediisocyanate, hydrogenated tolylene diisocyanate, hydrogenateddiphenylmethane diisocyanate, hydrogenated tetramethylxylenediisocyanate, and 4,4′-dicyclohexylmethane diisocyanate.

Examples of the aromatic polyisocyanates include 2,4-tolylenediisocyanate, 2,6-tolylene diisocyanate, 4,4′-diphenylmethanediisocyanate, 2,4′-diphenylmethane diisocyanate, 2,2′-diphenylmethanediisocyanate, 4,4′-diphenylether diisocyanate,2-nitrodiphenyl-4,4′-diisocyanate,2,2′-diphenylpropane-4,4′-diisocyanate,3,3′-dimethyldiphenylmethane-4,4′-diisocyanate, 4,4′-diphenylpropanediisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate,naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate,3,3′-dimethoxydiphenyl-4,4′-diisocyanate, xylylene-1,4-diisocyanate, andxylylene-1,3-diisocyanate.

The polyfunctional isocyanate compound may also be a dimer or trimer ofany of the aliphatic polyisocyanates, alicyclic polyisocyanates,aromatic polyisocyanates, and aromatic aliphatic polyisocyanates, andspecifically, the polyfunctional isocyanate compound may be a dimer ortrimer of diphenylmethane diisocyanate, a reaction product oftrimethylolpropane and tolylene diisocyanate, a reaction product oftrimethylolpropane and hexamethylene diisocyanate, or a polymer such aspolymethylene polyphenylisocyanate, polyether polyisocyanate, orpolyester polyisocyanate.

Commercially available products of the polyfunctional isocyanatecompound may also be used, examples of which include CORONATE L (tradename, manufactured by Nippon Polyurethane Industry Co., Ltd.) as atrimer adduct of trimethylolpropane and tolylene diisocyanate, andCORONATE HL (trade name, manufactured by Nippon Polyurethane IndustryCo., Ltd.) as a trimer adduct of trimethylolpropane and hexamethylenediisocyanate.

Examples of the polyfunctional melamine compound include methylatedmethylolmelamine and butylated hexamethylolmelamine, and examples of thepolyfunctional epoxy compound include diglycidyl aniline and glycerindiglycidyl ether. One of these may be used, or two or more of these maybe used in combination.

While the type or added amount of the crosslinking agent is notrestricted, the crosslinking agent should be added so that beforeexposure to radiation, a pressure-sensitive adhesive layer with a gelfraction of 20 to 80% by weight, preferably 30 to 70% by weight can beformed in a pressure-sensitive adhesive sheet for applications wherepeeling is performed through heating. If the gel fraction is less than20% by weight, a moderate degree of cohesive strength may fail to beobtained, which may be a cause of staining or adhesive deposit duringpeeling. A gel fraction of more than 80% by weight is not preferred,because at such a gel fraction, the pressure-sensitive adhesive layermay have a high initial elastic modulus, be less tacky, and have areduced initial adhesive strength, so that the function of thepressure-sensitive adhesive may decrease.

For example, the added amount of the crosslinking agent is preferablyfrom 0.001 to 20 parts by weight, more preferably from 0.001 to 10 partsby weight, based on 100 parts by weight of the polyester composition(which means the polyester when only the polyester is used with nobranched polyester oligomer). If the added amount is less than 0.001parts by weight, the process of forming the pressure-sensitive adhesivelayer may fail to increase cohesive strength. An added amount of morethan 20 parts by weight is not preferred, because with such an amount,the resulting pressure-sensitive adhesive layer may fail to havesufficient adhesive strength and may have reduced adhesive strength.

A catalyst may also be used as appropriate to efficiently control thegel fraction of the pressure-sensitive adhesive layer before exposure toradiation, which is used to form the radiation-cure removable typepressure-sensitive adhesive sheet of the invention. Examples of thecatalyst include tetra-n-butyl titanate, tetraisopropyl titanate,butyltin oxide, and dioctyltin dilaurate.

The added amount of the catalyst is preferably, but not limited to, 0.01to 1 part by weight, more preferably 0.05 to 0.5 parts by weight, basedon 100 parts by weight of the polyester composition (the polyester or amixture of the polyester and the branched polyester oligomer). If theadded amount is less than 0.01 parts by weight, the added catalyst mayfail to be effective, and an added amount of more than 1 part by weightis not preferred, because such an amount may significantly reduce shelflife and coating stability.

The polyester-based pressure-sensitive adhesive composition for formingthe pressure-sensitive adhesive layer for use in the invention may alsocontain a combination of the crosslinking agent and a tackifying resin,which makes it possible to obtain a pressure-sensitive adhesive layerhaving the desired properties.

The tackifying resin is not restricted and may be any conventionallyknown one, examples of which include a terpene-based tackifying resin, aphenol-based tackifying resin, a rosin-based tackifying resin, analiphatic petroleum resin, an aromatic petroleum resin, acopolymer-based petroleum resin, an alicyclic petroleum resin, a xyleneresin, an epoxy-based tackifying resin, a polyamide-based tackifyingresin, a ketone-based tackifying resin, and an elastomer-basedtackifying resin. In particular, a rosin- or terpene-based tackifyingresin produced from a plant-derived raw material is preferably used sothat the biomass degree can be increased. One of these may be used, ortwo or more of these may be used in combination.

Examples of the terpene-based tackifying resin include a terpene resin,a terpene phenol resin, and an aromatic modified terpene resin, andspecific examples that may be used include an α-pinene polymer, aβ-pinene polymer, a dipentene polymer, and modifications thereof, suchas a phenol-modified terpene-based resin, an aromatic modifiedterpene-based resin, a hydrogenated modified terpene-based resin, and ahydrocarbon-modified terpene-based resin.

Examples of the phenol-based tackifying resin that may be used includecondensation products of formaldehyde and any of various phenols such asphenol, m-cresol, 3,5-xylenol, p-alkylphenol, and resorcin. Furtherexamples that may be used include resols obtained by addition reactionof formaldehyde and any of the phenols in the presence of an alkalicatalyst; novolac resins obtained by condensation reaction offormaldehyde and any of the phenols in the presence of an acid catalyst;and rosin-modified phenolic resins obtained by addition reaction ofphenol with any of rosins such as unmodified or modified rosin andderivatives thereof and thermal polymerization of the addition product.

Examples of the rosin-based tackifying resin include a rosin resin, apolymerized rosin resin, a hydrogenated rosin resin, a rosin esterresin, a hydrogenated rosin ester resin, and a rosin phenol resin.Specific examples that may be used include unmodified rosin (raw rosin)such as gum rosin, wood rosin, or tall oil rosin, modified rosinobtained by hydrogenation, disproportionation, polymerization, or anyother chemical modification thereof, and derivatives thereof.

The added amount of the tackifying resin is preferably from 10 to 100parts by weight, more preferably from 15 to 80 parts by weight, inparticular, preferably from 20 to 60 parts by weight, based on 100 partsby weight of the polyester composition (the polyester or a mixture ofthe polyester and the branched polyester oligomer). If the added amountis less than 10 parts by weight, the desired adhesive strength may failto be obtained, and a pot-life effect may also fail to be produced. Anadded amount of more than 100 parts by weight is not preferred, becausewith such an amount, the crosslinking effect based on the addition ofthe crosslinking agent may be insufficient, and the compatibility withthe polymer component (the polyester composition) may also be degraded,so that a problem such as a reduction in adhesive strength may occur.

As far as the properties of the pressure-sensitive adhesive layer(pressure-sensitive adhesive) for use in the radiation-cure removabletype pressure-sensitive adhesive sheet of the invention are notdegraded, the polyester-based pressure-sensitive adhesive compositionused to form the pressure-sensitive adhesive layer may also contain anyof common additives such as ultraviolet absorbers, photostabilizers,peeling regulators, plasticizers, softening agents, fillers, colorantssuch as pigments and dyes, antioxidants, and surfactants.

In a preferred mode, the polyester-based pressure-sensitive adhesivecomposition is produced using a plant-derived raw material. This isbecause the plant-derived raw material, which is biodegradable and saidto be so-called carbon neutral, can form a globalenvironmentally-friendly or environmentally-sound, pressure-sensitiveadhesive. The composition preferably has a biomass degree of 50% ormore, more preferably 60% or more, which is a measure of how muchplant-derived material the composition contains. As used herein, theterm “biomass degree (%)” means the plant-derived material content,which is the calculated ratio of the weight of the plant-derived rawmaterial(s) used to the total weight of the raw materials used to formthe polyester-based pressure-sensitive adhesive composition. Examples ofthe plant-derived raw material include a dimer acid, sebacic acid or thelike for the dibasic acid component, lactic acid for the lactic acidcomponent, and 1,3-propylene glycol for the glycol (diol) component.

The pressure-sensitive adhesive layer is made from the polyester-basedpressure-sensitive adhesive composition. The use of the polyester-basedpressure-sensitive adhesive composition makes it possible to obtain aglobal environmentally-friendly pressure-sensitive adhesive layer withgood adhesive properties.

The pressure-sensitive adhesive layer preferably has a storage modulusof 1×10⁴ to 1×10⁷ Pa, more preferably 1×10⁵ to 1×10⁶ Pa, as measuredusing a dynamic viscoelasticity meter under the conditions of 23° C. anda frequency of 1 Hz. A storage modulus of less than 1×10⁴ Pa may causethe problem of a reduction in the cohesive strength and holding power ofthe pressure-sensitive adhesive layer. On the other hand, a storagemodulus of more than 1×10⁷ Pa is not preferred, because such a storagemodulus may cause the problem of hardening of the pressure-sensitiveadhesive layer and a reduction in pressure-sensitive adhesive strength.

For example, the thickness of the pressure-sensitive adhesive layer,which may be arbitrarily selected, is preferably from about 5 to about1,000 μm, more preferably from about 20 to about 500 μm, in particular,preferably from about 30 to about 200 μm. If the thickness of thepressure-sensitive adhesive layer is less than 5 μm, sufficient adhesivestrength may be difficult to obtain, so that peeling may easily occur. Athickness of more than 1,000 μm is not preferred, because with such athickness, the adhesive strength may increase with time, which may makepeeling difficult. The pressure-sensitive adhesive layer may be in theform of any of a single layer and a laminate.

The radiation-cure removable type pressure-sensitive adhesive sheet ofthe invention may be a pressure-sensitive adhesive sheet including thepressure-sensitive adhesive layer and a substrate (backing) provided onone side of the pressure-sensitive adhesive layer. Alternatively, it maybe a double-sided pressure-sensitive adhesive sheet (backing-less,single pressure-sensitive adhesive layer) formed using thepressure-sensitive adhesive layer directly with no substrate.Alternatively, it may be a double-sided pressure-sensitive adhesivesheet including a substrate and the pressure-sensitive adhesive layerplaced on each side of the substrate. As far as the characteristics ofthe radiation-cure removable type pressure-sensitive adhesive sheet ofthe invention are not degraded, an intermediate layer or an undercoatlayer can also be provided with no problem.

Examples of the substrate (backing) that may be used include appropriatethin materials such as a paper-based backing such as a paper sheet; afiber-based backing such as a fabric, a nonwoven fabric, a felt, or anet; a metal-based backing such as a metal foil or a metal sheet; aplastic-based backing such as a plastic film or sheet; a rubber-basedbacking such as a rubber sheet; a foamed product such as a foamed sheet;and laminates thereof (specifically including a laminate of aplastic-based backing and any other backing and a laminate of plasticfilms (or sheets)). In view of handleability and the like after heating,the backing preferably has high heat resistance so as not to melt at thetemperature of heat treatment of a thermally-expandablepressure-sensitive adhesive layer. A plastic-based backing such as aplastic film or sheet is preferably used as the backing. Examples of thematerial for such a plastic backing include an olefin-based resinincluding an α-olefin monomer component, such as polyethylene (PE),polypropylene (PP), an ethylene-propylene copolymer, or anethylene-vinyl acetate copolymer (EVA); polyester such as polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), or polybutyleneterephthalate (PBT); polyvinyl chloride (PVC); polyphenylene sulfide(PPS); an amide-based resin such as polyamide (nylon) or fully aromaticpolyamide (aramid); and polyether ether ketone (PEEK). These materialsmay be used alone or in combination of two or more. In a particularlypreferred mode, polylactic acid is used, which isglobal-environmentally-friendly, plant-derived material.

When a plastic-based material is used as the substrate (backing), itsdeformability such as elongation may be controlled by stretching orother processes. When a radiation-cure material is used as a foamingagent, a substrate that does not block radiation from passingtherethrough is used in a preferred mode.

The surface of the substrate (backing) may have undergone a commonsurface treatment for enhancing adhesion to the pressure-sensitiveadhesive layer (a thermally-expandable pressure-sensitive adhesive layeror any available non-thermally-expandable pressure-sensitive adhesivelayer for use in the invention, which may further contain a surfactant),such as a chromic acid treatment, exposure to ozone, exposure to aflame, exposure to a high-voltage electric shock, an ionizing radiationtreatment, or any other chemical or physical oxidation treatment, or acoating treatment with an undercoating agent. A coating treatment with arelease agent such as silicone resin or fluororesin may also beperformed to impart peelability from the thermally-expandablepressure-sensitive adhesive layer or the like.

If necessary, the substrate may contain any of various additivescommonly used in backings (substrates) for pressure-sensitive adhesivetapes, such as ultraviolet absorbers, photostabilizers, antioxidants,fillers, pigments, and dyes.

If necessary, the substrate may also be appropriately subjected to arelease treatment with any of release agents such as silicone-based,fluorine-based, long chain alkyl-based, and fatty acid amide-basedrelease agents or a silica powder; any of adhesion facilitatingtreatments such as an antifouling treatment, an acid treatment, analkali treatment, a primer treatment, a corona discharge treatment, aplasma treatment, and an ultraviolet treatment; or any of antistatictreatments such as coating-type, kneading-type, and vapordeposition-type antistatic treatments.

The thickness of the substrate (backing) may be arbitrarily selecteddepending on the material or shape of the substrate. For example, it ispreferably from about 1 to about 1,000 μm, more preferably from about 1to about 500 μm, even more preferably from 3 to 300 μm, in particular,preferably from 5 to 250 μm. A thickness out of the range may reduceworkability or processability and therefore is not preferred.

The method of forming the pressure-sensitive adhesive layer may be basedon a known pressure-sensitive adhesive sheet-manufacturing method,examples of which include, but are not limited to, a method includingapplying a pressure-sensitive adhesive composition (a solution of apressure-sensitive adhesive composition in a solvent or a hot melt of apressure-sensitive adhesive composition) to the substrate (backing) anddrying the coating to form a pressure-sensitive adhesive layer, a methodof transferring a pressure-sensitive adhesive layer formed on a releaseliner, a method of extruding and applying a pressure-sensitive adhesivelayer-forming material onto the substrate, a method of extruding thesubstrate and a pressure-sensitive adhesive layer in two or more layers,and a method of laminating the substrate with a singlepressure-sensitive adhesive layer. A co-extruding method or the like mayalso be used, in which a thermoplastic resin substrate and apressure-sensitive adhesive layer are extruded in two or more layers byinflation molding or T-die molding. Alternatively, a backing-less,double-sided, pressure-sensitive adhesive sheet may also be formed by aprocess including forming a pressure-sensitive adhesive layer on arelease liner and peeling off the pressure-sensitive adhesive layer fromthe release liner. In the invention, the pressure-sensitive adhesivesheet may also include a pressure-sensitive adhesive film, apressure-sensitive adhesive tape, a roll, or the like.

The pressure-sensitive adhesive composition (solution) may be appliedusing a conventionally known method such as roll coating, gravurecoating, reverse roll coating, roll brush coating, air knife coating,spray coating, or extrusion coating with a die coater or the like.

The release liner is not restricted, and any conventionally-knownrelease liner may be used as appropriate. For example, a productobtained by forming a release coating layer on one side of a releaseliner backing may be used. The release liner backing may be used in theform of a single layer or a plurality of layers.

Any of various thin materials such as plastic films, paper sheets,foamed products, and metal foils may be used as the release linerbacking. A plastic film is particularly preferred. Examples of thematerial for the plastic film include polyester such as polyethyleneterephthalate, polyolefin such as polypropylene or ethylene-propylenecopolymer, and thermoplastic resin such as polyvinyl chloride.

The thickness of the release liner backing may be selected asappropriate, depending on the intended use.

The release coating layer is not restricted, and anyconventionally-known release coating layer may be used. For example, acoating layer including an appropriate release agent such as a silicone,long-chain alkyl, or fluoride release agent may also be provided.

(Initial Adhesive Strength)

The radiation-cure removable type pressure-sensitive adhesive sheet ofthe invention has an initial adhesive strength of 1.4 N/20 mm or more,preferably 3 to 10 N/20 mm, at 23° C. and a peel angle of 180° withrespect to a stainless steel plate and at a peel rate of 150 mm/minute.An initial adhesive strength of less than 1.4 N/20 mm is not preferred,because such an adhesive strength is not sufficient to the adherend, sothat a trouble such as peeling may occur during use.

(Adhesive Strength after Exposure to Radiation)

After attached to the adherend (a stainless steel plate) and exposed to4,800 mJ radiation, the radiation-cure removable type pressure-sensitiveadhesive sheet of the invention can have an adhesive strength(post-irradiation adhesive strength) of 0.9 N/20 mm or less, preferably0.5 N/20 mm or less, at a peel angle of 180° with respect to thestainless steel plate and at a peel rate of 150 mm/minute. Apost-irradiation adhesive strength of more than 0.9 N/20 mm is notpreferred, because such an adhesive strength is too high so that afterthe pressure-sensitive adhesive sheet is used, an adhesive deposit maybe formed on the adherend in the process of peeling off the sheet, orthe sheet may be prevented from being peeled off from the adherend.

The radiation-cure removable type pressure-sensitive adhesive sheet ofthe invention can be widely used (substituted) for conventionallywell-known, radiation-cure, removable applications, and since its loadon the global environment is relatively small even when it is disposedafter use, it is preferably used in radiation-cure removable typepressure-sensitive adhesive sheet applications where the sheet is peeledoff and incinerated after use.

EXAMPLES

Hereinafter, the invention is described in more detail with reference tothe Examples, which are not intended to limit the invention. In theexamples, the term “parts” means “parts by weight.” The formulations andthe results of evaluation are shown in Tables 1. In Table 1, the contentof each monomer component used in the polyester synthesis is shown inunits of % by mole, and in Tables 2 and 3, each added amount is shown inparts by weight.

(Preparation of Polyester A)

To a reaction can equipped with a stirrer, a thermometer, and a draincondenser were added 86 parts of a dimer acid (PRIPOL 1009, manufacturedby Croda, 567 in weight average molecular weight), 10 parts of sebacicacid, 30 parts of 1,3-propylene glycol, 0.4 parts of trimethylolpropane,50 parts of DL-lactide, and 0.014 parts of tetrabutyl titanate and 0.014parts of tin octylate as polymerization catalysts. After the temperaturewas raised to 250° C. over 5 hours in a nitrogen atmosphere at normalpressure, the mixture was allowed to react for 1 hour, in whichesterification was performed while distilled water was removed out ofthe system. The pressure was further reduced to 10 mmHg over 30 minutes,and early-stage polymerization was performed at 250° C. for 30 minutes.The pressure was further reduced to 1 mmHg over 30 minutes, andlate-stage polymerization was performed at 250° C., so that a polyesterA was obtained. The formulation and the results of the evaluation areshown in Table 1.

(Preparation of Polyester B)

To a reaction can equipped with a stirrer, a thermometer, and a draincondenser were added 22 parts of L-lactide, 15 parts of DL-lactide, 54parts of ε-caprolactone, 0.2 parts of ethylene glycol, and 0.026 partsof tin octylate as a polymerization catalyst. After the temperature wasraised to 180° C. over 1 hour in a nitrogen atmosphere at normalpressure, the mixture was allowed to react for 3 hours, in whichesterification was performed while distilled water was removed out ofthe system. The pressure was further reduced to 1 mmHg over 10 minutes.The pressure was reduced at 180° C. over 30 minutes, so that the lactideresidue was removed, and a polyester B was obtained. The formulation andthe results of the evaluation are shown in Table 1.

Example 1

After 100 parts of the polyester A was dissolved in a mixed solvent of75 parts of methyl ethyl ketone (MEK) and 75 parts of ethyl acetate, 2parts of a polyvalent isocyanurate (TPA-100, manufactured by Asahi KaseiChemicals Corporation) as a crosslinking agent, 40 parts of anultraviolet (UV)-cure urethane oligomer (SHIKOH UV-1700B, manufacturedby The Nippon Synthetic Chemical Industry Co., Ltd.) as a radiation-cureresin, which has six unsaturated bonds per molecule and a weight averagemolecular weight of 2,000, and 5% by weight (2 parts) (based on theamount of the radiation-cure resin) of1-hydroxy-cyclohexyl-phenyl-ketone (IRGACURE 184, manufactured by CibaJapan K.K.) as a photopolymerization initiator were added to thesolution. The resulting mixture was applied onto a 25 μm thickpolyethylene terephthalate film (LUMIRROR 25S-10, manufactured by TORAYINDUSTRIES, INC.) as a substrate so that a 30-35 μm thick coating couldbe formed after drying. The coating was dried at 120° C. for 3 minutesand then bonded to the release-treated surface of a release-treatedpolyethylene terephthalate film. The resulting laminate was furtherallowed to stand (aged) at 50° C. for 3 days, so that a radiation-cureremovable type pressure-sensitive adhesive sheet was obtained.

Example 2

A radiation-cure removable type pressure-sensitive adhesive sheet wasobtained by the same process as in Example 1, except that 30 parts ofthe UV-cure urethane oligomer as a radiation-cure resin was addedinstead and that 5% by weight (1.5 parts) of the photopolymerizationinitiator was added based on the amount of the radiation-cure resin.

Example 3

A radiation-cure removable type pressure-sensitive adhesive sheet wasobtained by the same process as in Example 1, except that 70 parts ofthe UV-cure urethane oligomer as a radiation-cure resin was addedinstead and that 5% by weight (3.5 parts) of the photopolymerizationinitiator was added based on the amount of the radiation-cure resin.

Example 4

A radiation-cure removable type pressure-sensitive adhesive sheet wasobtained by the same process as in Example 1, except that 3% by weight(1.2 parts) of the photopolymerization initiator was added based on theamount of the radiation-cure resin.

Example 5

A radiation-cure removable type pressure-sensitive adhesive sheet wasobtained by the same process as in Example 1, except that 10% by weight(4 parts) of the photopolymerization initiator was added based on theamount of the radiation-cure resin.

Example 6

A radiation-cure removable type pressure-sensitive adhesive sheet wasobtained by the same process as in Example 1, except that 0.5 parts ofthe polyvalent isocyanurate as a crosslinking agent was added instead.

Example 7

A radiation-cure removable type pressure-sensitive adhesive sheet wasobtained by the same process as in Example 1, except that 3 parts of thepolyvalent isocyanurate as a crosslinking agent was added instead.

Example 8

A radiation-cure removable type pressure-sensitive adhesive sheet wasobtained by the same process as in Example 1, except that 8 parts of abranched polyester oligomer (Hyperbranched Polymer BOLTORN H40, 490mgKOH/g in hydroxyl value, 5,100 in weight average molecular weight) wasfurther added to 100 parts of the polyester A to form a polyestercomposition and that 6 parts of a polyvalent isocyanurate (TPA-100,manufactured by Asahi Kasei Chemicals Corporation) was added as thecrosslinking agent.

Comparative Example 1

A pressure-sensitive adhesive sheet was obtained by the same process asin Example 1, except that 20 parts of the UV-cure urethane oligomer as aradiation-cure resin was added instead and that 5% by weight (1 part) ofthe photopolymerization initiator was added based on the amount of theradiation-cure resin.

Comparative Example 2

A pressure-sensitive adhesive sheet was obtained by the same process asin Example 1, except that 80 parts of the UV-cure urethane oligomer as aradiation-cure resin was added instead and that 5% by weight (4 parts)of the photopolymerization initiator was added based on the amount ofthe radiation-cure resin.

Comparative Example 3

A pressure-sensitive adhesive sheet was obtained by the same process asin Example 1, except that 1% by weight (0.4 parts) of thephotopolymerization initiator was added based on the amount of theradiation-cure resin.

Comparative Example 4

A pressure-sensitive adhesive sheet was obtained by the same process asin Example 1, except that 15% by weight (6 parts) of thephotopolymerization initiator was added based on the amount of theradiation-cure resin.

Comparative Example 5

A pressure-sensitive adhesive sheet was obtained by the same process asin Example 1, except that 0.2 parts of the polyvalent isocyanurate as acrosslinking agent was added instead.

Comparative Example 6

A pressure-sensitive adhesive sheet was obtained by the same process asin Example 1, except that 5 parts of the polyvalent isocyanurate as acrosslinking agent was added instead.

Comparative Example 7

A pressure-sensitive adhesive sheet was obtained by the same process asin Example 1, except that 100 parts of the polyester B was added inplace of the polyester A.

The composition of each polyester and the results of the evaluation areshown in Table 1, and the composition of each pressure-sensitiveadhesive sheet produced using the polyester and the results of theevaluation are shown in Tables 2 and 3.

(Composition of Polyester)

The polyester was dissolved in chloroform-D, and the composition of thepolyester was analyzed by subjecting the solution to ¹H-NMR analysisusing a nuclear magnetic resonance (NMR) analyzer 400-MR manufactured byVarian, Inc.

(Molecular Weight)

The number average molecular weight (Mn) and the weight averagemolecular weight (Mw) were determined as described below. The polyestercomposition (the polyester or a mixture of the polyester and thebranched polyester oligomer) was applied onto a release-treatedpolyethylene terephthalate (PET) film so that a 100 μm thick coatingcould be formed after drying, and the coating was dried at 120° C. for 2hours so that the solvent was removed. The dried product was peeled offfrom the PET and used as a measurement piece. Subsequently, 0.01 g ofthe measurement piece was weighed and added to 10 g of tetrahydrofuran(THF) and allowed to stand for 24 hours so that it was dissolved. Thesolution was subjected to gel permeation chromatography (GPC) method,and each molecular weight was determined from the calibration curveobtained using polystyrene standards.

(Measurement Conditions)

Analyzer: HLC-8220GPC, manufactured by TOSOH CORPORATION

Sample injection volume: 20 μl

Eluent: THF

Flow rate (flow speed): 0.300 ml/minute

Measurement (column) temperature: 40° C.

Column: G6000H₆, manufactured by TOSOH CORPORATION

Column size: 7.5 mm ID×30.0 cm L

Detector: differential refractometer (R1)

(Glass Transition Temperature of Polyester)

The glass transition temperature (Tg (° C.)) was determined using adifferential scanning calorimeter (DSC-220 (product name), manufacturedby Seiko Instruments Inc.) under the following measurement conditions: 5mg of a measurement sample placed in an aluminum pan; temperature, −120to 150° C.; temperature rise rate, 20° C./minute.

(Hydroxyl Value of Polyester and Polyester Composition)

About 0.5 g of a sample of the polyester or the polyester compositionwas placed in a 250 ml Erlenmeyer flask and weighed. Subsequently, 20.00ml of a solution prepared by mixing acetic anhydride and anhydrouspyridine in a ratio of 1:10 (weight ratio) was taken and added to theErlenmeyer flask, and a condenser was attached thereto. The mixture wasrefluxed under stirring for 20 minutes and then cooled to roomtemperature. Subsequently, 20 ml of acetone and 20 ml of distilled waterwere added to the Erlenmeyer flask through the condenser. After aphenolphthalein indicator was added thereto, the mixture was titratedwith an aqueous 1.00 N (normal) sodium hydroxide solution. The hydroxylvalue (mgKOH/g) was calculated by subtracting the result of additionalmeasurement of a blank (containing no sample) from the result of thetitration.

(Acid Value of Polyester and Polyester Composition)

In 20 ml of chloroform was dissolved 0.2 g of a sample of the polyesteror the polyester composition. Using phenolphthalein as an indicator, thesolution was titrated with a 0.1 N (normal) potassium hydroxide-ethanolsolution, and the acid value (mgKOH/g) was calculated.

(Biomass Degree)

The percentage of the weight of the plant-derived raw materials used tothe weight of all raw materials used was calculated and used as thebiomass degree (%) in the evaluation.Biomass degree (%)=100×(the weight of the plant-derived raw materialsused)/(the weight of all raw materials used)

(Gel Fraction)

The pressure-sensitive adhesive sheet (with a 50 μm thickpressure-sensitive adhesive layer) obtained in each of the examples andthe comparative examples was cut into a 5 cm×5 cm square piece. The cutpiece sample was wrapped in a TEFLON (registered trademark) sheet whoseweight was known, and the total weight was measured. The wrapped samplewas allowed to stand in toluene at 23° C. for 7 days, so that the solfraction was extracted from the sample. Subsequently, the sample wasdried at 130° C. for 2 hours, and the dried weight was measured. The gelfraction was calculated from the following formula:gel fraction(%)={(the weight after drying−the weight of the TEFLONsheet)/(the weight before drying−the weight of the TEFLON sheet)}×100

(Storage Modulus)

The pressure-sensitive adhesive layer was formed on a release liner(MRF38, manufactured by Mitsubishi Polyester Film Corporation, 38 μm inthickness), and the pressure-sensitive adhesive layer was shaped into a3 mm thick, 8 mmφ diameter, test sample. Subsequently, the test samplewas sandwiched between parallel plates with a diameter of 7.9 mm (forshearing test), and the storage modulus (G′ (Pa)) of the sample wasmeasured at 23° C. using a viscoelasticity tester ARES manufactured byRheometric Scientific Inc., while shearing strain was applied thereto ata frequency of 1 Hz.

(Initial Adhesive Strength)

The pressure-sensitive adhesive layer (single layer) was prepared with athickness of 50 μm and bonded to one side of a polyethyleneterephthalate film (LUMIRROR 5-10, manufactured by TORAY INDUSTRIES,INC., 25 μm in thickness), so that a test sample of 100 mm long×20 mmwide was prepared. Subsequently, the test sample was bonded(press-bonded) onto a stainless steel plate (BA304, manufactured byNikkal Shoko K.K., 0.5 mm in thickness) as the adherend by onereciprocation of a roller under a pressure of 2 kg, and measured forinitial adhesive strength (N/20 mm, at a temperature of 23±2° C. and ahumidity of 65±5% RH) at a peel angle of 180° and a peel rate of 150mm/minute according to JIS C 2107.

(Adhesive Strength after Exposure to Radiation)

A test sample was prepared as in the case of the initial adhesivestrength test. The test sample was allowed to stand at a temperature of23±2° C. for 30 minutes and then irradiated with 4,800 mJ ultravioletlight. The adhesive strength after the exposure to the radiation(ultraviolet light) was measured by the same method as in the case ofthe initial adhesive strength test.

(Peeling Properties)

The pressure-sensitive adhesive layer (single layer) was prepared with athickness of 50 μm and bonded to one side of a polyethyleneterephthalate film (LUMIRROR, manufactured by TORAY INDUSTRIES, INC., 50μm in thickness), so that a test sample of 20 mm long×20 mm wide wasprepared. Subsequently, the test sample was bonded (press-bonded) onto astainless steel plate (BA304, manufactured by Nikkal Shoko K.K., 0.5 mmin thickness) as the adherend by one reciprocation of a roller under apressure of 2 kg. After standing at a temperature of 23±2° C. and ahumidity of 65±5% RH for 30 minutes, it was checked whether the testsample was fixed on the stainless steel plate. Subsequently, 4,800 mJultraviolet light was applied for 1 minute, and it was visually observedwhether the stainless steel plate was peeling from thepressure-sensitive adhesive sheet. The case where the stainless steelplate was peeling from the pressure-sensitive adhesive sheet wasexpressed by the mark “o,” and the case where the stainless steel platewas not peeling form the pressure-sensitive adhesive sheet was expressedby the mark “x” in the evaluation of the peelability of thepressure-sensitive adhesive sheet after the exposure to the radiation(ultraviolet light).

TABLE 1 Compositions for synthesis of polyesters (mol % ratio) andresults Polyester of evaluation of polyesters A B Dibasic acid Dimeracid 30 component Sebacic acid 10 Glycol 1,3-propylene glycol 39component Ethylene glycol 0.2 Trimethylolpropane 1 Lactic acidDL-lactide 20 51 Copolymerized ε-caprolactone 49 component Tg (° C.) −54−39 Hydroxyl value mgKOH/g 6 0.6 Acid value mgKOH/g 0.6 1.1 Weightaverage molecular weight (Mw) 153,000 83,000 Number average molecularweight (Mn) 29,000 49,000 Dispersity (Mw/Mn) 5.3 1.7

TABLE 2 Results of evaluation of polyester-based pressure-sensitiveExample adhesive composition 1 2 3 4 5 6 7 8 Polyester A 100 100 100 100100 100 100 100 Branched H40 8 polyester oligomer Crosslinking TPA-100 22 2 2 2 0.5 3 6 agent Catalyst OL-1 0.1 Radiation- UV-1700 40 30 70 4040 40 40 40 cure resin Radiation IRGACURE 5 5 5 3 10 5 5 5 reaction 184initiator Biomass wt % 68 73 56 69 66 69 67 64 degree Storage modulus×10⁵ Pa 2.3 2.3 2.2 2.3 2.3 2.3 2.3 2.3 (23° C.) Gel fraction wt % 45 4839 45 43 26 74 70 of pressure- sensitive adhesive layer Initial N/20 mm6.2 6.7 5.2 6.0 5.9 7.2 1.6 1.8 adhesive strength (before exposure toradiation) Adhesive N/20 mm 0.6 0.9 0.5 0.9 0.4 0.9 0.5 0.5 strengthafter exposure to radiation Peelability — ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ after exposureto radiation

TABLE 3 Results of evaluation of polyester-based pressure- sensitiveadhesive Comparative Example composition 1 2 3 4 5 6 7 Polyester A 100100 100 100 100 100 B 100 Crosslinking TPA-100 2 2 2 2 0.2 5 2 agentCatalyst OL-1 0.1 0.1 Radiation-cure UV-1700 40 80 40 40 40 40 40 resinRadiation IRGACURE 5 5 1 15 5 5 5 reaction 184 initiator Biomass degreewt % 79 53 70 64 69 67 20 Storage modulus ×10⁵ Pa 2.3 2.2 2.3 2.3 2.32.3 8.3 (23° C.) Gel fraction of wt % 49 36 45 42 12 91 30 pressure-sensitive adhesive layer (before exposure to radiation) Initial N/20 mm6.5 Bad 6.3 Bad Bad 0.9 1.3 adhesive appearance appearance appearancestrength (unmeasurable) (unmeasurable) (unmeasurable) (before exposureto radiation) Adhesive N/20 mm 2.2 6.2 0.3 0.4 strength after exposureto radiation Peelability — X — X — — Unfixable Unfixable after exposureto radiation

From the evaluation results in Table 2, it was demonstrated that in allof the examples, the characteristic values were each in the desiredrange, stable adhesive properties were provided before the irradiation,and good peelability (workability) was provided after the exposure toradiation. In addition, high biomass degrees of at least 56% by weightwere shown, so that global environmentally-friendly, radiation-cureremovable type pressure-sensitive adhesive sheets were successfullyobtained.

In contrast, from the evaluation results in Table 3, it was demonstratedthat in Comparative Example 1 where the amount of the radiation-cureresin was less than the specified amount, the reduction in adhesivestrength after the exposure to radiation was small, and the removabilitywas low. It was demonstrated that in Comparative Example 2 where theadded amount of the radiation-cure resin was more than the specifiedamount, it was not possible to uniformly mix the resin with thepolyester, so that the appearance of the pressure-sensitive adhesivelayer itself was degraded, which made impossible the evaluation of theremovability. It was demonstrated that in Comparative Examples 3 and 4where the radiation reaction initiator was not added in the specifiedamount, it was not possible to sufficiently reduce the adhesive strengthafter the exposure to radiation in Comparative Example 3, and theappearance of the pressure-sensitive adhesive layer itself was degradedso that the evaluation itself of the removability was impossible inComparative Example 4. It was found that in Comparative Example 5, themeasurement of the initial adhesive strength itself was not possiblebecause the added amount of the crosslinking agent was small so that thegel fraction was lower than specified. It was also demonstrated that inComparative Example 6, the initial adhesive strength was low so that thestability of the adhesive strength was not sufficient because the addedamount of the crosslinking agent was high so that the gel fraction washigher than specified. It was demonstrated that in Comparative Example 7where the polyester used did not contain any lactic acid component andthe hydroxyl value was out of the specified range, the biomass degreewas as very low as 20% by weight, and the initial adhesive strength wasalso low.

The invention claimed is:
 1. A radiation-cure removablepressure-sensitive adhesive sheet, comprising: a pressure-sensitiveadhesive layer made from a polyester-based pressure-sensitive adhesivecomposition comprising a polyester comprising at least a lactic acidunit, a dibasic acid unit, and a glycol unit, a radiation-cure resin, aradiation reaction initiator, and a crosslinking agent, wherein thedibasic acid unit comprises a dimer acid, the polyester has a weightaverage molecular weight of 20,000 to 200,000 and a glass transitiontemperature of −70 to −20° C. as measured using a differential scanningcalorimeter at a temperature rise rate of 20° C./minute, the polyesterhas a hydroxyl value of 1 to 60 mgKOH/g, the adhesive compositioncontains 30 to 70 parts by weight of the radiation-cure resin based on100 parts by weight of the polyester, the adhesive composition contains3 to 10% by weight of the radiation reaction initiator based on theamount of the radiation-cure resin, and wherein the pressure-sensitiveadhesive layer has a gel fraction of 20 to 80% by weight before exposureto radiation, and a storage modulus before exposure to radiation of1×10⁴ to 1×10⁷ Pa as measured using a dynamic viscoelasticity meterunder conditions of 23° C. and a frequency of 1 Hz.
 2. Theradiation-cure removable pressure-sensitive adhesive sheet according toclaim 1, wherein the polyester contains 10 to 50% by mole of the lacticacid unit and 50 to 90% by mole of components other than the lactic acidunit, and the molar ratio of the dibasic acid unit to the glycol unit is1:0.8 to 1:1.2.
 3. The radiation-cure removable pressure-sensitiveadhesive sheet according to claim 1, wherein the dibasic acid unitfurther comprises an aliphatic dibasic acid other than the dimer acid.4. The radiation-cure removable pressure-sensitive adhesive sheetaccording to claim 1, wherein the polyester comprises a tri- orpolyfunctional carboxylic acid and/or polyol component as a componentother than the lactic acid unit, the dibasic acid unit, and the glycolunit, and the polyester has a dispersity (Mw/Mn) of 2.5 to 10.0.
 5. Theradiation-cure removable pressure-sensitive adhesive sheet according toclaim 1, wherein the polyester has an acid value of 5 mgKOH/g or less.6. The radiation-cure removable pressure-sensitive adhesive sheetaccording to claim 1, wherein the radiation-cure resin has a part with amolecular weight of 100 to 10,000 between functional groups.
 7. Theradiation-cure removable pressure-sensitive adhesive sheet according toclaim 1, wherein the crosslinking agent is a tri- or polyfunctionalpolyisocyanate.
 8. The radiation-cure removable pressure-sensitiveadhesive sheet according to claim 1, which has an adhesive strength of1.4 N/20 mm or more before exposure to radiation, and has an adhesivestrength of 0.9 N/20 mm or less after exposure to radiation.